Hydrothermal process for growing crystals having the structure of beryl in highly acid chloride medium

ABSTRACT

A hydrothermal process for growing relatively large macrocrystals having the structure of beryl. Growth takes place on seed crystals from an aqueous medium which has a chloride ion concentration of at least 4 molar and contains sufficient hydrochloric acid to give a final pH of not greater than 0.1.

' United States Patent [19.

Yancey 51 Mar. 27, 1973 541 HYDROTHERMAL PROCESS FOR [561 ReferencesCited GROWING CRYSTALS HAVING THE UNITED STATES PATENTS STRUCTURE OFBERYL IN HIGHLY 3 34 302 9/1967 Fl 1 3 anigen eta. ..2 I30] ACIDCHLORIDE MEDIUM 3,567,643 3/1971 Flanigen et al. ..106/42 [75] Inventor:Pa l J eph Yan y, n Di go, 3,234,135 2/1966 Ballman et al.......252/62.58 Calif. 3,567,642 3/1971 Flanigen ..l06/42 [73] Assignee:Union Carbide Corporation, New THER PUBLICATIONS Y k, N.Y. r or ChemicalAbstracts, Vol. 41 p. 680 40 h Herbert t Smith Memorial Lecture Journalof Gemology, Vol. [22] F1 ed Aug 3,1970 p g 8845, (1961) [21] Appl. No.267,676

Related U.S. Application Data Continuation of Ser. No. 774,180, Nov. 7,1968, abandoned.

U.S. Cl. ..252/30l.4 F, 106/42, 23/301 SP, 23/304, 23/305 Int. Cl...C09k 1/54, BOlj 17/00 Field of Search ..252/301.4 F, 62.58, 62.59;106/42; 23/295, 301, 304, 305

Primary ExaminerEarl C. Thomas Assistant Examiner-J. Cooper AttorneyPaulA. Rose, Thomas I. OBrien, Leo A. Plum and Harrie M. Humphreys [57]ABSTRACT 6 Claims, No Drawings HYDROTHERMAL PROCESS FOR GROWING CRYSTALSHAVING THE STRUCTURE OF BERYL IN HIGHLY ACID CHLORIDE MEDIUM larl'y, itrelates to a process for growing large single crystals having thestructure of beryl of a size suitable for scientific and commercial usesfrom seeds in highly acidic aqueous chloride media at elevatedtemperatures and pressures.

' Beryl, which is the only ore of beryllium, is a crystal having theideal composition 3.0BeO-l .0Al O 6.OSiO and is commonly found in itsnatural form in granite. Its crystal structure is a hexagonal system,and it is usually found in the form of long, six-sided prisms. Theframework of the crystal structure of beryl is a complex cyclosilicatering structure in which the silicon atoms are at the centers of a groupof four oxygen atoms lying at the points of tetrahedra. Thesetetrahedral groups are linked together by the sharing of oxygen atoms inthe rings having the composition Si O The silica rings are joinedtogether by aluminum atoms lying in the center of a group of six oxygenatoms, and by beryllium atoms in a similar group of four oxygen atoms.There are two molecules in each unit cell. Beryl ranges in Mohs hardnessfrom 7.5 to 8, and in specific gravity from 2.63 to 2.85.

In addition to pure beryl, there are crystallographic analogs of berylwhich are also valuable for scientific and commercial uses. Thestructure of these analogs is essentially the same as that of beryl,except for the presence of small amounts of materials other than theoxides of beryllium, silicon and aluminum which are present. Forexample, when small amounts of aluminum are isomorphously replaced bychromium in the beryl crystal structure, a green crystallographic analogof-beryl is obtained which has essentially the same crystal structure ofberyl. The product thus obtained is commonly known as emerald, althoughgreen gemstone emeralds do not necessarily always contain chromium.

When a metal ion other than those of aluminum, silicon and beryllium isincorporated in small amounts in the structure of beryl, the crystalwhich is thus obtained is commonly known in the art as a doped crystal.For example, when small amounts of chromium are incorporated in thecrystal structure of beryl, the resulting emerald which is obtainedcould be considered to be a chromium-doped beryl. The ion thusincorporated in the crystal structure is usually referred to as a dopantion. For example, in the case of synthetically grown emerald orchromium-doped beryl the chromium which is incorporated in the syntheticcrystal would be considered to be the dopant ion. Thus, the terms doped"and dopant are well-known in the art and are intended to have the abovedefined and well known meanings whenever they appear hereafter in thisapplication.

The principal object of the present invention is to provide a processfor synthesizing single crystals having the structure of beryl,particularly beryl analogs doped with transition metal or rare earthmetal ions.

Another object is to provide synthetic crystals or beryl structure,particularly those doped with transition metal or rare earth metal ionswhich are of a size suitable for use in the gemstone art and insolid-state devices.

Other and further objects and advantages of the present invention andthe preferred embodiments thereof will become apparent .and aredisclosed in detail in the following description.

The process of the present invention represents an improvement over apreviously known method for hydrothermal growth of beryl and analogs ofberyl; namely, the method for carrying out such growth in an acidichalide medium described in British Patent 1,094,931. In particular, theprocess of the present invention provides increased yields of newgrowth, increased growth rate of beryl, and improved beryl crystalquality over those obtainable by the method of British Patent 1,094,931.

The present invention relates to a hydrothermal process for growingsingle crystals having the structure of beryl which comprises depositinga composition having the structure of beryl on a seed crystal from anaqueous reactant mixture which comprises (1) at least a major amount of(a) sources 'of oxides of beryllium, aluminum and silicon and (b) anaqueous medium which contains chloride ions in a concentration of atleast 4 molar and contains sufficient hydrochloric acid to give a final(after the hydrothermal reaction has taken place) pH of not greater than0.1 and,-optionally, (2) a minor amount of sources of ions of one ormore dopant transition metals and/or rare earth metals, the processbeing operated at a temperature of at least 400 C. and under a pressureof at least 6,000 pounds per square inch.

The transition metals useful in the process of this invention are thosehaving atomic numbers from 21 through 31 inclusive; 39 through 49,inclusive; and 72 through 78 inclusive. The rare earth metals useful inthe process of this invention are those having atomic numbers from 57through 71, inclusive. A preferred group of transition metals comprisesvanadium, chromium, manganese, iron, cobalt and nickel; these dopantelements impart highly desirable color characteristics to gemstonecrystal products of this invention. A preferred group of rare earthmetals comprises neodymium, samarium, gadolinium and europium becausethese dopant elements impart particularly desirable optical propertiesto crystals for use in solidstate devices.

Since the process'of this invention is a hydrothermal process which isconducted at elevated temperatures and pressures, the process is mosteasily conducted in a sealed reaction vessel, autoclave or bomb of atype well known in the hydrothermal art of crystal synthesis. A varietyof these reaction vessels are commercially available and are highlysuitable for use in practice of this invention. The reaction vesselwhich is employed should be constructed of a high strength,corrosion-resistant steel or alloy in order to withstand the pressuressilicon; maximum 1% manganese; maximum 0.8% carbon; balance nickel. Thereaction vessel is also preferably provided with a liner or capsule ofacid resistant metal, such as silver, platinum, gold or tantalum inorder to avoid corrosion of the vessel by the highly acidic medium whichis employed in the process of this invention. Several designs for highpressure reaction vessels are suitable for use in conducting the processof this invention, for example, those described by A. A. Ballman and R.A. Laudise (Hydro-thermal Growth," The Art and Science of GrowingCrystals, (1963) pp. 232-235], and a gold-lined or platinum-lined bombsimilar to that described by Morey in Amer. Miner. Vol. 22 pp. 1,121(1937). The bomb or capsule should remain tightly sealed throughout thereaction period in order to maintain the optimum conditions forsatisfactory growth and crystal clarity.

The silicon, beryllium and aluminum oxide sources (nutrients) which arepresent in the aqueous acidic reactant mixture are usually present inthe form of hydrous oxides of these metals. Any convenient source of theoxides of silicon may be employed as a starting material, such as forexample, optical grade quartz crystal, fused quartz, SiO porous glassand the like. The use of optical grade quartz crystal is preferred.Similarly as a source for the oxides of aluminum one may employmaterials such as sapphire, gibbsite Al,o,-H,o), aluminum hydroxidewhich has been precipitated from solutions of aluminum salts such asaluminum nitrate and the like. Convenient sources of the oxides ofberyllium are materials such as beryllium hydroxide [Be(OH) berylliumoxide, and the like. Although the composition of the reactant mixturewith respect to the oxides of silicon, beryllium and aluminum may varyover a wide range, a reactant mixture containing these oxides in amountswhich closely approximate the stoichiometric amount of these oxides inthe composition of the ideal beryl crystal (3.0BeO-l .OAl O 6.OSiO ispreferred.

When doped beryl crystals are prepared according to the present process,the source of the transition metal or rare earth metal ion dopant whichis present in the reactant mixture is a metal compound such as atransition metal or rare earth hydroxide, a transition metal or rareearth metal nitrate, a transition metal or rare earth metal oxide, atransition metal or rare earth metal chloride, a transition metal orrare earth metal sulfate and the like. The source of dopant ion may alsobe the elemental dopant metal.

Although it is theoretically possible to incorporate over l percent byweight ofa transition metal or a rare earth metal ion dopant into theberyl structure, lower weight percentages of dopant are normallyincorporated into the beryl crystal by the process of this invention.Depending primarily on the requirements dictated by the particular enduse of the crystal being grown, the concentration of transition metal orrare earth metal ion dopant in the crystal product may vary from about0.005 weight per cent to about 8 weight per cent, preferably 0.01 weightpercent to 2 weight percent, based on the total weight of the crystal.When the dopant ion is chromium, a concentration of 0.1 to 2 weightpercent is particularly preferred.

In order to provide an amount of transition metal or rare earth metalion dopant sufficient to produce crystals containing dopants in amountswithin the ranges of percentages set forth above, the reactant mixtureshould contain a metal ion concentration of from about 0.01 weightpercent to about 11 weight percent, based on the weight of berylequivalent to oxide in the nutrient of aluminum, silicon and berylliumin the ini tial charge. Preferably, the concentration of transitionmetal or rare earth metal ion from the compound is from 0.01 weightpercent to 2 weight percent, based on the theoretical weight of berylfrom the oxide sources. More than one transition metal or rare earthmetal ion may be used simultaneously as a dopant in the initial charge.

The aqueous chloride medium employed in the process of this inventioncontains chloride ions in a concentration of at least 4 molar and has afinal pH of not greater than 0.1. The term final pH" means the pH of thereaction mixture employed in the process of this invention after thehydrothermal reaction has been completed and the reaction mixture hasbeen cooled to 25 C. It is necessary to define the acidity of thereaction mixture in this manner because a certain amount of reactiontakes place between the hydrochloric acid present and the sources ofberyllium, aluminum, and silicon which reduces the hydrogen ionconcentration present in solution prior to carrying out the hydrothermalreaction process.

The reactant mixture employed in the process of the present invention ismost conveniently prepared by first placing the sources of oxides ofberyllium, aluminum, and silicon and the seed crystal or crystals in thereaction vessel, and then adding thereto an aqueous solution containinghydrogen chloride or hydrogen chloride plus other sources of chlorideion, such as ammonium chloride. The amount of hydrogen chloride andother source of chloride ion should be sufficient to provide a totalchloride ion concentration of at least 4 molar, and the amount ofhydrogen chloride should be sufficient to provide a final pH of notgreater than 0.1. A certain amount of reaction will then take placebetween the aqueous hydrogen chloride and the sources of oxides ofberyllium, aluminum, and silicon. Some of this reaction may take placeimmediately upon addition of the aqueous solution, for example, areaction between aluminum hydroxide and hydrochloric acid, whileadditional reaction will take place during the hydrothermal synthesisreaction at elevated temperature and pressure.

In a preferred form of the process of this invention the concentrationof chloride ion in the aqueous reactant mixture is at least 8 molar.

In a particularly preferred embodiment of the process of the inventionthe aqueous reactant mixture includes only the sources of oxides ofberyllium, aluminum, and silicon (and, optionally, sources of dopantions) and aqueous hydrochloric acid, that is, the aqueous hydrochloricacid provides both the minimum concentration of chloride ion of4 molarand the high acidity necessary to provide a final pH of not greater than0.1.

It has also been found that when chromium is being used as the dopantion, it is highly desirable that the acidic aqueous reactant mixtureshould be substantially free of fluoride ion, in order to avoidprecipitation of metal fluorides such as chromium fluoride which areinsoluble and form precipitates under the acidic conditions of thepresent process. The presence of insoluble metal fluoride salts causesinclusions and cloudiness in the resulting crystals which are obtained,hinders the incorporation of the chromium ion dopant into the crystalexcept as occluded particles, and affects the rate of growth adversely.

In practicing the process of the present invention .the synthetic berylor doped beryl is grown on a seed crystal located within the sealedreaction vessel. The nutrient oxides and dopant ions migrate to theregion of the seed, and new growth crystallizes thereon. Although anycrystal having the structure of beryl or other suitable substrate may beused as a seed, a seed crystal of natural or synthetic beryl or a berylanalog is usually employed. Normally, the reaction is continued untilthe new growth is thick enough to be cut from the original seed. Thisnew growth may then be employed as a seed crystal in further subsequentreactions. In this way macro-crystals of beryl structure of onlysynthetic hydrothermal origin are obtained. This is particularly usefulin preparing macro-crystals of beryl structure having high purity anduniform composition arid structure. Large synthetic crystals may also beobtained by conducting a series of short-term runs wherein fresh oxidenutrient and solution are used in each run of the series. A highlyfavorable aspect of this invention is the ability to achieve andmaintain favorable growth rates over extended periods of time. Forexample, an average growth rate of greater than 0.8 mm. per day in thelength of an edge of a crystal has been maintained over a period of 7days, and an average of as high as 0.6 mm. per day has been maintainedover a period of 13 days.

Another favorable aspect of this invention is the ability tosubstantially confine growth of crystal having the structure of beryl tothe seed, and to obtain single crystal growth on such seed or seedswhich is substantially flawless and optically transparent. Spontaneousnucleation and twining on the surface of the seed are eliminated.

The present process for growing crystals having the structure of berylis generally conducted at temperatures of from about 400 C. to about 700C. and at pressures of from about 6,000 pounds per square inch to about30,000 pounds per square inch. Although it may be difficult to determinewith absolute accuracy the actual operating pressure for thehigh-pressure systems employed in the present process, the internalpressure within the reaction vessel can be calculated from knownpressure-temperature-volume data on water when low concentrations ofsolutes are present. Knowing the volume of the reaction vessel, thevolume of the reactant mixture and the reaction temperature, thereaction pressure can be most conveniently calculated by using thepressure-temperature-volume data for pure water published by G. C.Kennedy in American Journal ofScience, Vol. 248, p. 540 (1950).

It should also be understood that the upper limits of temperature rangeand particularly the pressure range are dependent to a great degree onthe equipment which is available, and that these upper limits might beextended if equipment could be designed to withstand the highertemperatures and pressures. With the equipment which is presentlyavailable, the reaction temperature is from about 400 C. to about 700C., and

the pressure is from about 6,000 pounds per square inch to about 30,000pounds per square inch. A temperature of from 550 to 650 C. and apressure from 15,000 pounds per square inch to 25,000 pounds per squareinch is preferred.

It has also been found that the growth rate may be accelerated somewhatby maintaining a temperature differential between the upper and lowerportions of the reaction vessel or bomb. This differential may beachieved by providing a separate heating element for the lower portionof the reaction vessel or bomb, and then positioning the reaction vesseland the heating element in a large furnace which is maintained at atemperature which is lower than that produced by the heating element. Inthis manner, a temperature differential is easily maintained by suitablecontrol of the bomb and the furnace heaters. A temperature differentialbetween the top and the bottom of the reaction vessel of from about 10C. to about C. may be employed. A differential of from 10 C. to about 50C. is preferred.

It has also been found that the rate of growth may be affected by thegeometry of the seed crystal and the oxide nutrient sources within thereaction vessel. For best results the seed crystal should be positionedat a point in the reaction vessel which is intermediate to the zonewherein the silica source is located and zone wherein the berylliumoxide and aluminum oxide sources are located. Throughout the reactionthe seed crystal and all of the oxide sources are in intimate contactwith the acidic aqueous reactant mixture. The relative distances betweenthe silicon oxide source, the seed crystal or crystals, and theberyllium and alu-' minum oxide sources have not been found to becritical. An arrangement which has been found to be highly suitable forgrowing single crystals of good quality at relatively high growth ratesis one in which the oxide sources of beryllium oxide and aluminum oxideare placed at the bottom of the reaction vessel, the silicon oxidesource is suspended by means of a wire or a porous gauze basket of noblemetal in the upper portion of the reaction vessel, and the seed crystalor seed crystals are suspended by means of a noble metal wire at a pointin between.

It is also possible to employ multiple groups of oxide sources and seedcrystals within a reaction vessel wherein individual sets of oxidesources and seeds are stacked" in separate arrangements within saidvessel and all are in contact with a common acidic aqueous reactantmixture. The number of sets which may be employed is determinedprimarily by the available volume of the reaction vessel. The stacked"system is not a preferred method for carrying out the process of thisinvention.

When crystals prepared according to the process of this invention areremoved from the reaction vessel after it has cooled, the surfaces ofthese crystals may be covered with other phases or impurities whichformed within the autoclave during cooling. Although these phases orimpurities are not substantial in quantity, any impurities may beremoved before use of the crystal product as a gemstone or in asolid-state device by washing with hot or cold dilute acid solutions andwater or by scraping the surfaces clean.

The crystals of beryl and doped beryl produced by the process of thisinvention often differ somewhat from the ideal stoichiometry for beryl,namely, 3.0BeO-l.0Al O 6.0SiO The crystals of chromium doped berylproduced by the process of this invention 5 are characterized by havingrefractive indices in the range of 1.57 to 1.58 and by exhibiting abrilliant red fluorescence when excited by radiation in the ultravioletand visible violet and blue region of the elecinches to 0.300 inchesduring this period.

EXAMPLE 3 The following examples illustrate variations in the method ofgrowing emerald as set forth in Example 2:

a. The reaction vessel was loaded with the nutrient materials as notedin Example 2, but the concentration of the aqueous hydro-chloric acidsolution in this run was 6 molar in acid. After 7 days at a temperatureof I 10 610 C. the aquamarine seed grew 31.6 carats of fair tro-magneticspectrum. However, the red fluorescence quality emerald. of the chromiumdoped beryl crystals of this invention The reaction vessel was loaded i29 grams l is not as intense as the red fluorescence of chromium minumhydroxide, 6.7 grams quartz 030 grams doped beryl produced by theprocess of British Patent c c l ifx and g i f 1m d O d along 1,094,931-with the aquamarine seed and 14 ml. of aqueous 12 A Particular advantageof the Single crystals of beryl molar HCl. In 8 days the seed grew 1 1.8carats of good structure of this invention is the utility of the dopedli i h green emerald crystals in solid-state applications. Suchapplications A vessel was loaded with 1.99 grams Be(OH) 2.3 oftenrequire that the crystal be free of crystal impergrams Al (OI-U 6,0grams quartz, 0.15 gram CrCl -,'6H fections and contain only acontrolled amount of do- 0, d 13,5 l f aqueous 7 m l h d hl i id, pantion or ions homogeneously distributed throughout D i a i d f 4 d at anaverage temperature f the crystal structure and be substantially free ofun- 585 C thg Seeds grew 61) carats f d li li h desirable extraneousimpurities, such as flux inclusions. green emerald. Naturally-occurringcrystals of beryl structure such as d. Seven reactors were each loadedwith the reactant emeralds almost always contain at least small amountscharge described in Example 2. One aquamarine wafer of several impurityions. In addition, the level of exand one pure synthetic emerald seedwere hung in each traneous ions is often considerably out of the rangevessel and 14.1 ml of aqueous 12 molar hydrochloric desired forsolid-state applications. acid was added. The reactors were heated andcon- Following are examples of the practice of the inventrolled attemperatures between 620 and 630 C. for tion which is hereinbeforedescribed. In all of the fol- 3O 10 days. A total of 286.6 carats ofchromium doped lowing examples, the reactant mixture charge occupiedberyl were grown on the seeds during these runs. about 50 volume percentof the total reactor (pressure vessel) volume. EXAMPLE 4 This exampleillustrates the effect of chloride ion EXAMPLE 1 concentration in theprocess of this invention. A series This example illustrates the methodand results of f five runs was made in which each of five pressuregrowing undoped beryl.,A pressure vessel was charged vessels ofidentical dimensions was charged with a sinwith 2.7 grams berylliumhydroxide, 2.9 grams alugle aquamarine seed, all five seeds being ofapproximinum hydroxide, 6.7 grams crushed quartz, and an m ely the aWeight and z t g th r ith 2.7 aquamarine seed. No dopant ion wassupplied to the grams of beryllium hydroxide, grams aluminum system. Tothis mixture 14 ml. of aqueous l2 molar Hydroxide, grams Crushed q gramsof hydrochloric acid was added and the vessel was sealed. Cr CI '6I-IQOand 14 ml. of aqueous hydrochloric acid The vessel was then heated andheld to a temperature of varying concentrations. All five reactionvessels of 610 C for 11 days. The resulting growth on the aquamarineseed was 22.7 carats of perfectly clear,

were then heated for identical periods of 7 days. The results aresummarized in the following table.

Seed weight (g.)

Average vessel temp.

Normality Growth Color 0! Run Initial Final Bottom Top of H01 Final pHquality new growth 0. 3. 63 609 556 4 Almost clear. 0. 65 6. 98 608 5406 Very llghtgreen. 0.62 6. 18 610 547 8 Green. 0. 59 6. 64 609 659 10 0.5 0. 59 7. 75 608 570 12 0 d0 Darkgreen.

colorless, good-quality beryl.

EXAMPLE 2 This example illustrates the method and result of The abovedata show that at the minimum molarity of chloride ion (4 molar) and themaximum permissable final pH of 0.1 minimal growth of low qualitychromium doped beryl was obtained, while at chloride ion concentrationsof 8 molar or greater and at final pH's near zero, rapid growth ofexcellent quality chromium doped beryl was obtained.

EXAMPLE 5 This example compares the improved process of this inventionwith the prior process disclosed in British Patent 1,094,931.

Ten runs were carried out using the process of this invention, each runusing the same size pressure vessel, seed material and quantities ofreactants and temperatures employed in Example 4 except that 12 normalhydrochloric acid was used in all runs. An additional nine runs werecarried out in the same manner except that 5 normal aqueous ammoniumchloride was used in place of 12normal hydrochloric acid. Five normalammonium chloride is the preferred reaction medium disclosed in BritishPatent 1,094,931. All 19 reaction vessels were heated at thetemperatures employed in Example 4 for identical periods of 13 days.

Growth of chromium doped beryl was obtained on all 19 seed crystals. Forthe runs carried out using the process of this invention, all of the newgrowth was of excellent quality, the average amount of new growth oneach seed was 29.4 carats, and the average thickness of new growth onthe seed crystals was 5.50 mm. For the nine runscarried out using theprocess of British Patent 1,094,931 the new growth was of less goodquality, the average new growth on each seed crystal was 17.5 carats,and the average thickness of new growth on the seed crystals was 3.65mm.

EXAMPLE 6 The following examples illustrate the production of berylcrystals doped with a variety of metal ions. In these examples theloading procedure, reactants and reaction conditions were identical withthose of Example 1 except for the addition of various sources of dopantions.

a. To the charge specified in Example 1, 0.18 gram of V50 was added. Thenew beryl growth on the seed was analyzed by spectr ographic methods andwas found to contain greater than 0.10 weight percent vanadium as adopant ion.

b. To the charge specified in Example 1, 0.20 gram of MnO was added. Theresulting new beryl growth was found to contain greater than 0.1 weightpercent of manganese as a dopant ion.

c. To the charge specified in Example 1, 0.15 gram each of Mn0 and V 0was added. The resulting new beryl growth was found to contain in excessof 0.1 weight percent each manganese and vanadium as dopant ions.

d. To the charge specified in Example 1, 0.143 gram of Fe O was added.The resulting new beryl growth was found to contain greater than 0.1weight percent iron as dopant ion.

What is claimed is:

1. A hydrothermal process for growing single crystals having thestructure of beryl which comprises: depositing a composition having thestructure of beryl on a seed crystal from an acidic aqueous reactantmixture consisting essentially of; (l) at least a major amount of (a)sources of oxides of beryllium, aluminum and silicon, and (b) a chloridesolvent medium which contains chloride ions in a concentration of atleast 4 molar and which consists essentially of sources of chloride ionsand hydrochloric acid in an amount to give a final pH of not greaterthan 0.], and (2) up to minor amounts of sources of one or more ofthedopant metals vanadium, chromium, manganese, iron, cobalt, nickel,neodymium, samarium, gadolinium and europium; said process being carriedout at a temperature of at least 400 C. and under a pressure of at least6,000 pounds per square inch.

2. he process in accordance with claim 1 wherein said sources of oxidesof beryllium, aluminum and silicon are present in amounts which providesubstantially the stoichiometric amounts of beryllium, aluminum andsilicon oxides in the composition of an ideal beryl crystal (3.0 BeO-1.0 A1 0 6.0 SiO 3. The process in accordance with claim 1 wherein saidacidic aqueous reactant mixture consists essentially of (a) sources ofthe oxides of beryllium, aluminum and silicon, (b) hydrochloric acid,and (c) minor amounts of sources of ions of one or more of the dopantmetals vanadium, chromium, manganese and iron.

4. The process in accordance with claim 3 wherein said dopant metal ischromium.

5. The process in accordance with claim 3 wherein (1) said sources ofoxides of beryllium and aluminum are disposed near the bottom ofa closedreaction vessel, said sources of oxides of silicon are disposed near thetop of said vessel, and said seed crystal has the structure of beryl andis supported between said sources of oxides of beryllium and aluminumand said sources of oxides of silicon, and (2) wherein the temperatureat the bottom of said reaction vessel is at least 10 C. higher than thetemperature at the top of said vessel.

6. The process in accordance with claim 5 wherein said aqueous reactantmixture is substantially free from fluoride ion and wherein said sourceof dopant metal is CrCl 6 H 0 which is present in said reactant mixturein sufficient amount to supply from 0.01 to 2 weight percent chromiumion in said crystal based on the weight of ideal beryl crystaltheoretically equivalent to the weight of aluminum, beryllium andsilicon oxides present in said oxide sources.

2. The process in accordance with claim 1 wherein said sources of oxidesof beryllium, aluminum and silicon are present in amounts which providesubstantially the stoichiometric amounts of beryllium, aluminum andsilicon oxides in the composition of an ideal beryl crystal (3.0 BeO .1.0 Al2O3 . 6.0 SiO2).
 3. The process in accordance with claim 1 whereinsaid acidic aqueous reactant mixture consists essentially of (a) sourcesof the oxides of beryllium, aluminum and silicon, (b) hydrochloric acid,and (c) minor amounts of sources of ions of one or more of the dopantmetals vanadium, chromium, manganese and iron.
 4. The process inaccordance with claim 3 wherein saId dopant metal is chromium.
 5. Theprocess in accordance with claim 3 wherein (1) said sources of oxides ofberyllium and aluminum are disposed near the bottom of a closed reactionvessel, said sources of oxides of silicon are disposed near the top ofsaid vessel, and said seed crystal has the structure of beryl and issupported between said sources of oxides of beryllium and aluminum andsaid sources of oxides of silicon, and (2) wherein the temperature atthe bottom of said reaction vessel is at least 10* C. higher than thetemperature at the top of said vessel.
 6. The process in accordance withclaim 5 wherein said aqueous reactant mixture is substantially free fromfluoride ion and wherein said source of dopant metal is CrCl3 . 6 H2 Owhich is present in said reactant mixture in sufficient amount to supplyfrom 0.01 to 2 weight percent chromium ion in said crystal based on theweight of ideal beryl crystal theoretically equivalent to the weight ofaluminum, beryllium and silicon oxides present in said oxide sources.